Other
Montana State University: Line Integrals
A thorough explanation of line integration and how to represent force fields, include graphs and diagrams for visual reference and examples.
Curated OER
Educational Technology Clearinghouse: Maps Etc: Northeast China, 1971
"Northeast China - the provinces of Heilungkiang, Kirin, and Liaoning - is the most important region of the country and a nationally significant and still-developing center of agricultural production. Most of the Northeast remained...